Bleaching compositions have long been used in households for the bleaching and cleaning of fabrics. Liquid bleaches based upon hypochlorite chemical species have been used extensively, as they are inexpensive, highly effective, easy to produce, and stable. However, the advent of modern synthetic dyes and the use of modern automatic laundering machines have introduced new requirements in bleaching techniques, and have created a need for other types of bleaching compositions. In order to satisfy this need, and to broaden and extend the utility of bleaches in household use, other bleach systems have been introduced in recent years.
Of particular interest recently have been dry bleaching compositions based upon peroxyacid chemical species. Peracid chemical compositions have a high oxidation potential due to the presence of one or more of the chemical functional group: ##STR1##
In addition to active oxidizing agents, it is also desirable to provide one or more enzymes for the purpose of stain removal. Enzymes have the ability to degrade and promote removal of certain soils and stains by the cleavage of high molecular weight soil residues into low molecular weight monomeric or oligomeric compositions readily soluble in cleaning media, or to convert the substrates into different products. Enzymes have the substantial benefit of substrate specificity: enzymes attack only specific bonds and usually do not chemically affect the material to be cleaned. Exemplary of such enzymes are those selected from the group of enzymes which can hydrolyze stains and which have been categorized by the International Union of Biochemistry as hydrolases. Grouped within the hydrolases are proteases, amylases, lipases, and cellulases.
Enzymes are somewhat sensitive proteins which have a tendency to denature (change their molecular structures) in harsh environments, a change which can render the enzymes ineffective. Strong oxidant bleaches such as organic peracids adversely affect enzyme stability, especially in warm, humid environments in which there is a concentration of oxidant bleaching species.
Various methods to stabilize enzymes and provide a good mixture of enzyme and detergent or bleach have been proposed. Enzymes have variously been attached to carriers of clay, starch, and aminated polysaccharides, and even coglutinated to detergent carriers. Enzymes have been granularized, extruded, encased in film, and provided with colorizing agents. Attempts have been made to enhance enzyme stability by complexing the enzymes with proteins, by decreasing the relative humidity of the storage environment, by separating the bleach into discrete granules, and by the addition of reducing agents and pH buffers. However, the instability of enzymes in peroxyacid bleach compositions has continued to pose a difficulty, especially in the long-term storage of peroxyacid bleach compositions in which enzymes and bleach are in intimate contact.